The present invention relates generally to drive means for marine vessels and, more particularly, to improved boat drives of the inboard-outboard variety.
For many years power boats were generally grouped into two categories, i.e., "outboard" and "inboard". The "outboard" type of boat, powered by a self-contained power drive unit mounted to the transom of the vessel, was commonly considered to be of a smaller and lighter type of boat then the "inboard" which was powered by a large internal combustion engine driving a propeller either directly through an intermediate gear box or through a drive shaft extending through the bottom of the boat.
Eventually, the inherent advantages in outboard-type propeller drives were recognized and the state of the art progressed to the point where it was feasible to manufacture drive units to be mounted outboard of a boat, but which were coupled to a source of motive power disposed within the boat itself. Thus, a hybrid drive system, termed the "inboard-outboard" drive came into being.
The inboard outboard drive mechanism, however, posed substantial problems. While it was desired to be able to adjust the drive both to cant it to its optimum attitude and to rotate it for steering purposes, much in the manner of an outboard motor arrangement, the drive must be large and rugged enough to absorb the power transmitted by large inboard-mounted engines. To reconcile these requirements, several approaches have been taken by the prior art. Commonly, the upper portion of the drive unit is hinged so that its attitude may be adjusted relative to the stern of the boat. Universal joints are interposed in the power input shaft for transmitting power from a fixed shaft extending either directly from the motor, or through a transmission attached thereto, to the input mechanism of the drive unit. Further, in order to achieve directional control the drive unit may also be gimbaled at the same point so that the entire outboard-mounted unit may be turned. In the past, turning has been achieved by providing external hydraulic cylinders attached to the transom of the boat and extending to an appropriate portion of the drive unit casing. By turning a sterring wheel, the operator of the boat controls a source of hydraulic pressure which in turn operates the hydraulic cylinders at the stern, causing the drive unit to turn and thus effect a change in the direction of the driven vessel.
The hydraulic units heretofore used for steering have commonly been adapted from automotove applications, and have typically comprised certain of the hydraulic elements from a power steering apparatus. While such units have proved adequate for many types of operation, their external mounting necessarily exposes them to injury and damage. Further, especially in salt water usage, the hydraulic elements are susceptible of corrosion which hampers their efficacy and materially shortens their useful life.
In another type of known drive unit, the unit is divided into an upper and a lower section, and a hinge apparatus provided so that the lower section may rotate relative to the upper section in order to provide directional control. This simplifies the drive system mounting, though posing steering control problems similar to those presented by the afore-described arrangement.
In U.S. Pat. No. 3,605,677 -- Bergstedt there is disclosed a boat drive arrangement comprehending a steering control apparatus which overcomes some of the above-described problems. However, the hydraulically-driven rack arrangement requires custom-built dual-acting cylinders of rather complex design, and moreover necessitates a considerable increase in the width of the drive unit which increases the projected area thereof.
It will therefore be appreciated that it would be advantageous to provide a simplified, compact steering means for achieving directional control of an inboard-outboard drive, the elements of which are protected from corrosion and damage.
It is therefore an object of the present invention to provide an inboard-outboard drive unit having a superior directional control mechanism.
It is another object of the present invention to provide an inboard-outboard drive having an improved steering apparatus enclosed therewithin.
It is still another object of the invention to provide an improved steering apparatus in an inboard-outboard drive unit which is compact enough to fit within the drive unit housing.